docs: def is_valid_combination(row):
      """
      This is a filtering function. Filtering functions should return True
      if combination is valid and False otherwise.
  
      Test row that is passed here can be incomplete.
      To prevent search for unnecessary items filtering function
      is executed with found subset of data to validate it.
      """
  
      n = len(row)
  
      if n > 1:
          # Brand Y does not support Windows 98
          if "98" == row[1] and "Brand Y" == row[0]:
              return False
  
          # Brand X does not work with XP
          if "XP" == row[1] and "Brand X" == row[0]:
              return False
  
      if n > 4:
          # Contractors are billed in 30 min increments
          if "Contr." == row[3] and row[4] < 30:
              return False
  
      return True